During the manufacture of semiconductor wafers, the edge of the wafer is ground to a rounded or beveled profile by means of an abrasive wheel. The rounded edge reduces chipping during later process steps. The grinding wheel usually contains diamond abrasive ranging in particle size from 30 to 40 micrometers, and leaves a surface that has visible ridges and valleys as seen under a low power microscope. It is known that a smoother edge surface is needed in integrated circuit manufacturing. Smoother edges are needed because wafers with rough edges chip more easily, edge ground wafers contain deeper micro cracks than edge polished wafers, and edge ground wafers contain depressions that may be a source of particles in processes that use phosphorous glasses. Edge ground wafers sometimes cause photoresist to form "beaded" edges, i.e. photoresist does not spin correctly to make a uniform layer at the edge of the wafer, but makes an irregular thickened bead around the wafer edge. The beaded edge causes problems such as particle formation.
Present polishing processes include mechanically abrading wafers with a finer abrasive, dipping the wafer in an acid polishing mixture, treating the wafer edges with an acid polishing mixture, or by dripping or spraying an etchant onto the edge. Mechanical abrasion has the disadvantage that it does not produce a mirror finish. Dipping the entire wafer in acid leads to the rounding of the planar surfaces of the wafer unless extreme care is exercised in the process. Acid etching of the edge requires considerable removal of material for etching a smooth surface, which causes a problem with maintaining an optimum profile for the wafer.
Individual processing of single wafers is time consuming and costly. Some edge polishers carry wafers between threaded shafts, but these wafers have to be individually loaded and unloaded.